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The thing is, everyone wants fast for cheap and since a psu won't make you fast the layman will purchase an inexpensive unit. Inexpensive units to not live up to expectation in most cases, thus the exorbitant suggestion of a 750w psu.

..just a stab in the dark.

p.s. I would run 7970's in xfire without blinking with my current psu. It's all about quality.

p.s. I would run 7970's in xfire without blinking with my current psu. It's all about quality.

lol, it's all about quality but lets not exaggerate that much. You surely have a $170 550W PSU but two 7970 CF=500W peak, lets say 80W for HDDs/fans/motherboard and 100W for the CPU. How would that work for you?

It is conceivable that 650 watts of continuous loading is safe for the unit but hey, 500+80+100=680W, probably too risky i would say. But hey, it's yours to do what you want.

p.s. I would run 7970's in xfire without blinking with my current psu. It's all about quality.

nah, you wouldn't. 45.5A on the +12v rail. Yeah I guess you could, if you kept everything at stock, but then you're limiting yourself big time in performance. a good overclock on a 7970 (talking around 1200/1600 or above) will draw a lot of power.

there is an easy way to figure out if your power supply is good enough...
A gpu can use no more than 300w max. Unless you have a super overclock and are running furmark or intense compute apps you will NEVER get to 300w with an otherwise properly functioning card.

Typical tdp of a cpu is between 77-125 watts for high end cpus from amd and intel. server cpus from intel can get up to 140ish and the obnoxious fx9000 series from amd can sit at 225w tdp. but chalk those off the list for now.

tdp is the absolute max something can draw under normal usage scenarios.

ANY decent 550 watt power supply or higher will support ANY cpu/single gpu setup. Providing there are enough amps on the +12v rail(s). Ideally I always go for a power supply with a single strong +12v rail it makes high amperage a sure thing. amps+volts=watts.

when i got my corsair tx650 im using back in maybe 2006-2007ish i only got the 650 because it was 3$ more than the 550.

lol, it's all about quality but lets not exaggerate that much. You surely have a $170 550W PSU but two 7970 CF=500W peak, lets say 80W for HDDs/fans/motherboard and 100W for the CPU. How would that work for you?

It is conceivable that 650 watts of continuous loading is safe for the unit but hey, 500+80+100=680W, probably too risky i would say. But hey, it's yours to do what you want.

Quote:

Originally Posted by eclap

nah, you wouldn't. 45.5A on the +12v rail. Yeah I guess you could, if you kept everything at stock, but then you're limiting yourself big time in performance. a good overclock on a 7970 (talking around 1200/1600 or above) will draw a lot of power.

I'm glad you guys are so sharp.

Really, I was just trying to make a point but your points are certainly valid.

I don't have another card to test it with, but I'd surely do it with confidence. Just not with 1200MHz core clocks.. Stock for sure.

Just installed a little 450W (Silverstone ST45SF 450W) in my mates PC which is running a 2600K OC and the 280X without a problem. This is a good quality little guy. My general rule of thumb for PSU is if it's not reviewed and reviewed well on JonnyGuru don't get it I had a cheap 750W Corsair PSU that cooked some kit a while back and from then on its been good component PSU only. So good 450W plus will be fine for what you want.

I think some of these manufacturers list overkill wattage requirements because they assume the average PC user is not buying a top of the line modular PSU with XXX amount of continuous power. So if a card really requires a good 400W PSU (whole system included), the manufacturer might say it requires 550W, just to be on the safe side for the general consumer! Then a run of the mill cheapo "550W" PSU could run it w/absolutely no problem.

Quote:

Originally Posted by PieEyedPiper

I'd imagine a suggestion like that is complete nonsense.

The thing is, everyone wants fast for cheap and since a psu won't make you fast the layman will purchase an inexpensive unit. Inexpensive units to not live up to expectation in most cases, thus the exorbitant suggestion of a 750w psu.

..just a stab in the dark.

p.s. I would run 7970's in xfire without blinking with my current psu. It's all about quality.

On a 550W? You would start blinking when your PSU sets fire to your entire PC from overloading it with two 7970's lol. You may not want to go by this guys advice OP.

Just installed a little 450W (Silverstone ST45SF 450W) in my mates PC which is running a 2600K OC and the 280X without a problem. This is a good quality little guy. My general rule of thumb for PSU is if it's not reviewed and reviewed well on JonnyGuru don't get it I had a cheap 750W Corsair PSU that cooked some kit a while back and from then on its been good component PSU only. So good 450W plus will be fine for what you want.

Lol...go play FarCry3 for 4hrs on high in DX11 then see if you still think like that.

OK, you saw your mates rig was "running OK" ...great, but doesn't mean it "will run OK".
Overworked PSU's often run just fine.......right up to when they shut down due to overloading, overheating, or overcurrent protection tripping.
Ofc that doesn't always happen either, it may be smaller issues like BSOD, constant reboots, slow post, freezing, lag or choppy fps while gaming.....artifacts.....things like that...without reaching critical mass.

PSU's can be good quality for different reasons, some are efficient, some have fantastic voltage regulation, ripple suppression, or maybe impessive continuous power output on underspec'd units.
None of this will help though if your asking it to to a job it wasn't designed for - he has a gaming rig not an HTPC..

To be honest, you've given your friend a rather mediocre PSU with inadequate power. Another point to note is he has no wattage headroom for upgrading in the future.

Silverstone do make great units as you said, but unfortunately this isn't one of them, it failed 80+ Bronze efficiency tests, has substantial droop under crossloading and uses Teapo caps.

Your mates rig is going to draw maybe ~400W in a decent gaming session, factor which means once heat and droop are taken into account your 450W SS will be constantly working at near 100% capacity.

PSU's work best and last longest when they have headroom, there is no set rule but 20% seems to be the generally accepted figure.....

If it was my mate I'd replace that PSU with something a bit more up to the challenge...maybe the ST55F or one of the new CoolerMaster GX units - they're pretty good now that Seasonic make them.....

Actually I just saw you're in Australia, which means AcBel is another option you should consider. Not the low end crap they make but the M8/R8 M9/R9. They are seriously good bang for buck, I own 3 of them oldest is 7yrs never missed a beat.

Well, I saw this post, so I will ask here, 4 way Crossfire X with R9 280X Toxic will work fine with a 1200W psu like the Corsair AX1200i? or Sapphire Pure 1250W? Or I really need more? Like EVGA SuperNOVA NEX 1500? Also, which is the difference between the 2 evga 1500w? all seems the same except some letter and the 100 Price.

Well, I saw this post, so I will ask here, 4 way Crossfire X with R9 280X Toxic will work fine with a 1200W psu like the Corsair AX1200i? or Sapphire Pure 1250W? Or I really need more? Like EVGA SuperNOVA NEX 1500? Also, which is the difference between the 2 evga 1500w? all seems the same except some letter and the 100 Price.

First can I ask why you want to run quadfire? Are u familiar with quadfire scaling?